The present invention relates to an ink jet recording method.
An ink jet recording method is known wherein ink ejected from a nozzle of recording head is deposited on a recording material. In such an ink jet recording method, various method is used to improve the printing quality. As one method, ink having an adjusted penetration property are used. For example, in order to improve print density of characters or line images or to form sharp images, the use is made with ink having a low penetration speed into the recording material or sheet, thus providing a large amount of ink on the surface of the recording material, and in another example, the use is made with ink having a high penetration speed to increase the fixing speed.
The ink exhibiting a low penetration speed is called xe2x80x9ctopping type inkxe2x80x9d or xe2x80x9cnon-penetrative inkxe2x80x9d, since a large amount of the ink remains on the surface of the recording paper. The ink exhibiting a high penetration speed is called xe2x80x9cultra-penetrative inkxe2x80x9d.
When a droplet 51 of such an ultra-penetrative ink is dropped on the recording material, the amount of the ink remaining on the surface of the recording material 52 is small since it penetrates into the recording material immediately after contacted to the recording material 52. The penetration speed is high, and the ink may reach the neighborhood of the back side of the recording material 52, depending on the material of the sheet 52.
When the non-penetrative ink having less penetration property (topping type ink) is used, as shown in FIG. 46, (b), the component of the ink such as the solvent or the like tends to evaporate, and therefore, a relatively small part of the ink droplet 53 on the recording material 52 penetrates in the direction of the thickness of the recording material 52.
When the ultra-penetrative ink is used, the ink contacted to the surface of the recording paper quickly penetrates, with the result of less mixture with another ink, and therefore, less spread at the boundary portion with different color ink, However, the ink penetrates deep into the recording material, and is scattered in a long range, with the result that coloring matter component such as pigment or dye is dispersed, and that light incident on the recording material is reflected at a relatively deep position, and therefore, the density of the printed image seems low. In the plane of the recording material, the ink is scattered wide around the ink droplet 51 with the result of too large size of the recording dot and/or of spread in the form of whiskers around the dot((feathering) and therefore unsharp image.
When the on-penetrative ink is used, the amount of the ink remaining on the surface is relatively large, and therefore, the recording density is high, and when one dot is considered, the amount of the ink scattered in the recording material is very small as compared with the ultra-penetrative ink, so that sharp images can be formed. However, the penetration speed into the recording paper is low with the result that longer time is required to fix the ink, and therefore, whom another ink is deposited adjacent thereto, the inks flow to between them, with the result of spread occurring at the boundary portion therebetween and therefore of the deterioration of the image quality. When the surface of the recording sheet is rubbed with another recording paper or pen or the like, the ink fixed on the surface of the recording paper may be removed, or when the printed portion is overwritten by a line marker or the like, the ink is dissolved with the result of spread on the surface of the recording paper(poor wear resistance).
In view of such respective natures, it is usual to use black ink having a low penetration property and the other color inks having high penetration property. Since black color is frequently used when letter or line image which is desired to be looked sharp is printed, the non-penetrative ink is used for black color, since then a high density and a sharp edge is provided. In the case of chromatic printing wherein fine lines or dots are less frequently printed, and different color dots are printed adjacent to each other frequently, the ultra-penetrative ink is used for chromatic color since then the spread is less at the boundary between different colors.
Even if this is done, however, when the black dot 54 and the color dot 55 are adjacent to each other, the inks flow into between the dots with the result of deteriorated recording quality. The ink droplet of the black ink remaindering on the surface of the recording material discharges out into the color ink across the boundary portion 56, and correspondingly, the density of the boundary portion 56 of the black ink decreased, with the result that edge of the black ink dot becomes unsharp. In the color ink side, the black ink is mixed into the boundary portion 56 with the result of unsharp edge, too. When the different penetrative inks are adjacent to each other, the occurrence of the breeding at the 56 resulting in the poor recording quality has not been avoidable.
By leaving the-recording sheet for a long term after black ink ejection, the low penetrative ink can be fixed without breeding. This requires long time between the ejection of the black ink and the ejection of the color ink, and therefore, the throughput decreases. It is known that in order to raise the fixing speed, the recording material is heated by the heater. For example, a heater is provided at a position corresponding to a recording position of the recording head behind the recording surface of the recording material, by which the water content of the ink droplet deposited on the surface of the recording paper is evaporated, thus increasing the fixing speed. However, with such a method, water vapor is produced, and it may dew an the inside of the recording device and may adversely affect the recording material, a control circuit or a voltage source circuit of the recording device. It would be considered that water vapor is discharged to the outside of the apparatus by exhausting means, but then, the cost will rise, and the capacity of the voltage source of the apparatus has to be increased. When the recording material is heated by a heater at a high temperature, safety should be taken into consideration.
In order to ease the problem relating to the penetration property, use of recording material having been subjected to a special treatment would be considered. However, use of plain paper is desirable from the standpoint of cost or convenience of the user.
As described above, when the use is made with a so-called ultra-penetrative ink having a high penetration property, the spread at the boundary can be reduced, but the recording density decreases (unsharp image). When the use is made with so-called topping type ink having low penetration property, it is possible to record a sharp image with high recording density, but the time required for the fixing is long, and the problems of the bleeding and low wear resistance arise. When the topping type ink is used, and for the color image, ultra-penetrative ink is used, the bleeding occurs between the black ink dot and another color ink dot when they are adjacent.
Accordingly, it is a principal object of the present invention to provide an ink jet recording method by which improved fixing property, improved recording density, reduction of the spread at the boundary between the different color ink droplets, and the improved wear resistance of the image, are accomplished simultaneously.
According to an aspect of the present invention, there is provided an ink jet recording method using a recording device including a recording head provided with an ejection outlet for ejecting ink and heating means for heating at least a part of a recording material; comprising: a recording step of recording by ejecting ink to a predetermined region on a recording material, using a recording head; a heating step of heating said region by heating means; and wherein the ink has an ink absorption coefficient Ka (ml.mxe2x88x922.msecxe2x88x92xc2xd) relative to a plain paper, defined by Bristow method, is 1.0-5.0, and satisfies 0 less than tsxe2x89xa6200 msec where ts is a rapid expansion start point. According to this aspect, the spread at the boundary can be suppressed.
According to another aspect of the present invention, there is provided an ink jet recording method using a recording device including a recording head provided with an ejection outlet for ejecting ink and heating means for heating at least a part of a recording material; comprising: a first recording step of recording by ejecting ink to a predetermined region on a recording material; a heating step of heating said region by heating means; and a second recording step of recording by ejecting ink to said region after said heating step.
According to this aspect, the fixing device which heats the recording material at a relatively low temperature, and the improved recording density, the reduction of the spread at the boundary between the different color ink droplets and the improved wear resistance, are accomplished.
According to a further aspect of the present invention, there is provided an ink jet recording method using a recording device including a recording head provided with an ejection outlet for ejecting ink and heating means for heating at least a part of a recording material; comprising: a recording step of recording by ejecting ink to a predetermined region on a recording material, using a recording head; a heating step of heating said region by heating means; and wherein the ink satisfies 0 less than tsxe2x89xa6200 msec where ts is a rapid expansion start point. According to this aspect, the penetration of the penetrative ink is confined at a position inside the recording paper and adjacent the recording surface, and the ink is fixed, by which the improved recording density, the reduction of the spread at the boundary of the ink droplet, are accomplished, and since the ink droplet is penetrated into the recording paper, the resultant image has high wear resistance.